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2006 Merc 115 EFI Fuel Pressure Problems

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megus

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I have a 2006 Merc 115 that I am having fuel pressure issues with. Under power @ 3000 RPM it shows a 40 psi when you first start. It will run for about 20 minutes at this pressure and then it will start to fall off. It drops to 35, then 30 then 25 and the motor starts to studder and then it will fall all the way off and the motor dies.

If I try to start it back up immediately, it will not run. If I wait for about 5 minutes, it will start back up, but will only run about 3 or 4 minutes and then the fuel pressure starts to fall and the same problem again.

If I wait several hours, then try again, it will run again for about 20 minutes before the pressure drops.

Any suggestions?
 
Hmmm, that's a good question.

The battery is a new one. Are you saying to check the voltage put out by the motor to recharge the battery? Or just check the voltage of the battery?

I was also wondering. Is it possible that the VST could be running out of fuel at some point and causing the fuel pressure to drop?
 
So you have a YamaMerc. Your problems are all in the VST tank. Time to pull the tank and change the filter. I would also recommend pulling the injectors and the fuel rail and have them cleaned.
 
Chris, I have already pulled the fuel rail and changed the injectors. It ran for 45 minutes under power before the fuel pressure began to fall off and die today. The motor is on a houseboat in a remote location on the lake and its hard to work on while on the water. Is there anything I can do to improve the VST tank until the next time the boat is removed from the Lake? I'm not sure I can remove the tank while it is in the water.
 
There is no short cut, The VST has to come off to be serviced. The injector cleaning just completes the job. The whole intake has to come off to get to the VST. You will not be doing this while the boat is floating.
 
OK, VST Cleaned. Injectors cleaned. Boat runs for 20 minutes like a champ. Not a problem. Then, it slowly slows down and dies.

It seems to act like its out of fuel. It seems like there is no fuel getting into the VST when it gets hot. (103 degrees on lake) Could it be getting hot and vapor keeping fuel from entering VST?
 
Also, I've tried several times. When its cold, first out, it runs great for 20 minutes. Then dies. Next day, same thing. After its hot, I can wait 5 minutes and it will run again for about 3 or 4 minutes and die again.

Is there a possible heat problem in the VST?
 
Megus, I would love to know what you found out.

I have a 2007 Mercury EFI with very similar issues. The motor starts fine and runs like new, effectively until I stop and let it return to idle. Then it becomes a whole different motor. It then seems to run like it is running out of gas. It sputters and shakes and won't run over 2000 rpm without sputtering like crazy. I've managed to limp back to my dock a couple of times.

Thing is that after a start from cold, it almost doesn't seem to matter whether I run it for 5 minutes or 15. It will run well at 3500-4000 until I drop it back to idle. After that, it is a disaster. It is the act of dropping it back to idle that almost seems to reset something, and then it runs like crap.

Sound familiar? What did you end up doing??
 
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Faztbullet,
Thanks for the note. I can see how my poorly worded post might point to that. What I should have included is that after running it for a while and I return to idle, the idle is a bit rough but it doesn't remind me of the classic IAC issue where it stalls or has variable rpm. It is when I increase the rpms that it really screws up, shutters and sounds fuel starved. Perhaps that is still the IAC but the issue occurs, or is more noticeable with the motor is under the slightest amount of load.

I should mention that this is all on the heels of having some fuel supply issues -- I had just had a kinked fuel line under the tank which had been restricting fuel considerably - now fixed. I am wondering if this over time, stressed the fuel pump to the point to the point of failure and now I need to replace fuel pump - This still doesn't explain why it only occurs after running the engine for a while.
Jim
 
sorry to jump on this thread that is several months old but i have a friend that has a 2008 115 optimax that wont idle if he wants to troll he can the motor just dies out in idle any suggestions?
 
Sorry not to get back with people on this.

This was the solution:

New fuel filter to VST Tank.

Clean VST tank AND screen on bottom of High Pressure Fuel pump.

New fuel injectors.

Engine runs like new.

Second engine on Houseboat developed the same issues, and was also solved by same solution.

We now do this service at the beginning of the year on both engines to make sure they run great all year.
 
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